New surveillance data from PAHO reveals a striking disparity between vaccine effectiveness and real-world coverage across the Americas. The DTP vaccine demonstrates 95% protection against diphtheria when the full primary series is administered, yet rising case notifications indicate many populations have fallen dangerously below the 85-90% coverage threshold required for herd immunity. This gap between potential and actual protection highlights systemic challenges in vaccine delivery and uptake. Incomplete vaccination series—receiving only one or two doses instead of the full three-dose primary course—provides only 60% protection, leaving millions at risk. The data underscores that vaccination coverage, not vaccine efficacy, is the limiting factor in disease prevention. PAHO’s June 2026 statement emphasises that closing these coverage gaps through strengthened immunisation programmes is critical to preventing further diphtheria resurgence in the region.
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